A lung nodule found on a CT scan is almost never cancer — but it deserves expert assessment, not months of anxious waiting. This guide explains exactly what a lung nodule is, how risk is assessed using validated clinical scoring models, what the T-stage survival data shows, and what your options are.
Last reviewed: May 2026 · Dr Lawrence Okiror FRCS(CTh) FRCSEd(CTh) · GMC 6150382
A lung nodule is a rounded area of density within the lung up to 3cm in diameter. Over 95% are benign — caused by old infection, scar tissue, or non-cancerous growth.
Size, morphology, density, growth, and validated scores — including the Herder model on PET-CT — determine how concerning a nodule is. Expert review goes beyond the written report.
IASLC data shows T1a (≤1cm), T1b (>1–2cm), T1c (>2–3cm) carry meaningfully different five-year survival rates of 92%, 83%, and 76%. From 1cm to 3cm, every centimetre counts.
A lung nodule — sometimes called a pulmonary nodule, a lung shadow, or a spot on the lung — is one of the most common incidental findings in modern medical imaging. It is defined as a roughly round or oval opacity measuring 3cm or less in its longest dimension. Anything larger than 3cm is classified as a lung mass, which carries a higher probability of malignancy and warrants more urgent investigation.
Nodules appear on CT scans as white or grey areas against the dark background of normal aerated lung tissue. They vary considerably in their characteristics — some are solid and well-defined, others have a hazy, part-solid or ground-glass appearance. These characteristics, alongside size, location, and clinical history, all contribute to the assessment of how likely a nodule is to be significant.
The critical point is that a CT scan cannot reliably distinguish between a benign nodule and an early lung cancer on appearance alone. That is why expert clinical assessment matters — and why the appropriate response to a lung nodule is neither panic nor dismissal.
The majority of lung nodules are caused by the body's response to a previous infection or irritant and have nothing to do with cancer. The most common benign causes include:
Granulomas — the most common cause of benign nodules. A granuloma is a small cluster of immune cells that forms in response to infection, most commonly from organisms such as Mycobacterium tuberculosis or certain fungi. Many people carry granulomas without ever having had a symptomatic infection. Once the immune response resolves, the granuloma may calcify — calcified nodules are almost always benign and can usually be confirmed as such on imaging alone.
Hamartomas — the second most common benign lung nodule. Hamartomas are non-cancerous tumours composed of normal lung tissue elements arranged abnormally. They are entirely benign and grow very slowly. On CT, their characteristic appearance — including fat or popcorn calcification — often allows confident diagnosis without biopsy.
Scar tissue — previous lung infections, including pneumonia or pleuritis, can leave areas of scar tissue that appear as nodules on CT. These are entirely benign and stable over time.
Intrapulmonary lymph nodes — small lymph nodes that sit within the lung tissue itself. These are benign and require no treatment.
Early lung cancer — a minority of lung nodules represent primary lung cancer at an early, operable stage. Less commonly, a nodule may represent a metastasis from a cancer arising elsewhere. Where metastasis is a concern given the clinical history, this changes the investigative and treatment pathway significantly. Lung nodules and cancer →
15%
People in lung cancer screening found to have nodules
~1 in 278
People invited to screening ultimately diagnosed with lung cancer†
75%+
Screen-detected cancers found at early Stage I or II
Lung nodules are extremely common. Studies suggest that up to 50% of adults who have a CT scan of the chest for any reason will have at least one pulmonary nodule identified. In the context of the NHS Lung Cancer Screening Programme, around 15 in every 100 people scanned have nodules detected.
Five-year implementation data published in Nature Medicine in March 2026 (Lee et al.) confirms a profound shift in the stage at which lung cancer is being found. Among the 2 million-plus people invited to the programme, 7,193 lung cancers were diagnosed — approximately 1 in 278 of those invited. This statistic carries an important caveat: the denominator is participants invited to the programme, not those who actually attended for scanning. The detection rate among people who completed their CT scan is therefore meaningfully higher than 1-in-278. The headline figure should be understood in this context.
The finding that matters most is this: over 75% of screen-detected lung cancers are now found at Stage I or II — the stages at which surgery is most effective and long-term survival most likely. Historically, fewer than 30% of lung cancers were found at these early stages. CT screening has substantially reversed this. For patients with nodules found through the programme, see the targeted lung health check guide →
† Denominator is participants invited to the NHS Lung Cancer Screening Programme, not confirmed attendees. Lee et al., Nature Medicine, 23 March 2026.
Size is the single most important determinant of risk — but it is not the only one. British Thoracic Society guidelines provide a framework for how nodules of different sizes should be managed, based on their probability of malignancy.
| Nodule size | Risk category | Typical recommended approach |
|---|---|---|
| Under 5mm | Very low risk | No further investigation typically needed in low-risk individuals |
| 5–6mm | Low risk | Single follow-up CT at 12 months; discharge if stable |
| 6–8mm | Intermediate | Follow-up CT at 3 months; further assessment if growth or suspicious features |
| Over 8mm | Higher risk | MDT discussion; PET-CT; Herder score; consider biopsy or surgical resection |
| Over 30mm | Lung mass | Urgent investigation — malignancy must be excluded |
These thresholds are a guide, not a rigid protocol. A 7mm nodule with spiculated edges and a smoking history warrants more concern than a 9mm smooth, calcified nodule in a non-smoker. Size is assessed in the context of the full clinical picture — which is precisely why a written radiology report, however thorough, is not the same as expert specialist review of the images themselves.
When a lung cancer is diagnosed at Stage I, it is tempting to treat that as a single category and move directly to treatment planning. The TNM staging system is more nuanced than that — and understanding the nuance has direct implications for how urgently a nodule should be investigated and what operation is most appropriate.
The 8th edition of the IASLC staging manual (Rami-Porta et al., Journal of Thoracic Oncology, 2015) was based on 77,156 patients and introduced a critical refinement: Stage I was subdivided into three T1 categories based on tumour size alone. The principle underlying this was that size within Stage I predicts survival differently — and the data confirmed this definitively. Five-year survival rates by clinical stage:
T1a — Stage IA1
Tumour ≤ 1cm
92%
Five-year survival
clinical staging
T1b — Stage IA2
Tumour >1–2cm
83%
Five-year survival
clinical staging
T1c — Stage IA3
Tumour >2–3cm
76%
Five-year survival
clinical staging
These are not marginal differences. Between T1a and T1c — a difference of just 2cm of tumour size — the five-year survival gap is 16 percentage points. The new substage designations IA1, IA2, and IA3 were created specifically because the prognosis differs significantly enough to warrant separate classification.
Critically, this is not simply 8th edition data that has since been superseded. The 9th edition IASLC dataset (Van Schil et al., Journal of Thoracic Oncology, 2024) comprised 124,581 patients recruited between 2011 and 2019 — more than one and a half times the 8th edition cohort. The T-subcommittee analysed the data and reached a definitive conclusion: the T1 subdivisions perform adequately in the modern dataset. No revision to the T descriptors was proposed. The same cut-points — T1a, T1b, T1c — are retained in the 9th edition unchanged. The survival gradient holds across two independent datasets spanning over two decades of patient data and more than 200,000 patients.
The implication for a patient with a lung nodule is direct. A 9mm nodule that is ultimately found to be a T1a cancer at ≤1cm carries a 92% five-year survival after surgical resection — one of the best outcomes in oncology. A 25mm nodule that has grown to T1c carries 76%. Both are Stage I. Both are operable. But the difference between finding a cancer at 9mm versus 25mm is not trivial — it is approximately 16 percentage points of five-year survival. This is the clinical argument for not waiting months between CT surveillance scans when a more definitive assessment is available. The lung nodule precision pathway →
Smoking history — the most significant individual risk factor for lung cancer. Current and former smokers carry substantially higher risk than never-smokers. The risk persists for decades after stopping, though it diminishes progressively. Never-smoker lung cancers are a distinct biological entity — more commonly EGFR, ALK, or ROS1-driven — and GSTT has an active research programme in this area.
Age — lung cancer is rare under 40 and its incidence rises sharply with age. The NHS screening programme targets those aged 55 to 74 precisely because this is the age group in which screen-detected cancers are most likely to be found at an early, curable stage.
Family history — first-degree relatives with lung cancer independently increase individual risk, even in never-smokers.
Occupational and environmental exposure — asbestos, radon, silica, arsenic, and certain industrial chemicals are established lung carcinogens. Radon is the second leading cause of lung cancer in the UK after smoking.
Previous cancer history — individuals with a prior cancer diagnosis, particularly cancers with a propensity to metastasise to the lung (colorectal, breast, renal, melanoma, sarcoma), have a higher probability that a lung nodule represents a metastasis rather than a primary lung cancer.
Spiculated or irregular margins — nodules with a spiky or irregular border carry significantly higher malignancy risk than smooth, well-defined nodules.
Ground-glass opacity (GGO) — a hazy, semi-transparent appearance. Pure ground-glass nodules are often slow-growing but can represent early adenocarcinoma. Part-solid nodules — with both a ground-glass component and a solid core — carry higher risk than pure ground-glass lesions.
Upper lobe location — nodules in the upper lobes carry a higher probability of malignancy than those in the lower lobes, reflecting where tobacco-related cancers most commonly arise.
Growth on a previous scan — demonstrable growth between scans is the most significant indicator that a nodule warrants active investigation rather than continued surveillance.
Absence of calcification — calcified nodules, particularly those with dense central, laminated, or popcorn calcification, are almost invariably benign. Its presence is strongly reassuring.
The NHS surveillance pathway for intermediate-risk nodules typically involves repeat CT scans at three, six, and twelve-month intervals. For the majority of patients whose nodules are ultimately benign, this is entirely appropriate. But for those whose nodules are genuinely concerning, the interval between scans can represent a period of preventable delay. The modern question is not whether to watch — it is whether we have better tools to get an answer sooner. In many cases, we do.
Surveillance has a well-documented limitation: it establishes stability or growth retrospectively. By the time growth confirms malignancy, weeks or months have elapsed. The T-stage survival data makes the cost of this delay tangible — a nodule that measures 11mm at one scan and 23mm at the next has moved from a likely T1a to a likely T1c. The difference is not administrative. It is 16 percentage points of five-year survival.
Modern diagnostic tools have changed this equation for selected patients. Where a nodule warrants tissue diagnosis — because of its size, characteristics, or the patient's risk profile — ION robotic bronchoscopy can now reach and biopsy nodules that were previously inaccessible without surgery, often as a day case. For an intermediate-risk nodule, this can replace three rounds of CT surveillance with a single definitive answer.
Assessment of a lung nodule involves three layers: imaging review, clinical risk stratification, and — where indicated — tissue diagnosis.
The CT scan is the starting point. A specialist thoracic surgeon reviews the images — not just the report — assessing size, morphology, density, location, and any changes from previous imaging. At a first consultation, Dr Okiror reviews CT scan images personally alongside the written report, forming an independent assessment. The images contain more information than any written summary of them.
At Guy's and St Thomas', all cases with indeterminate or suspicious nodules are discussed at a specialist multidisciplinary team (MDT) meeting involving thoracic surgeons, thoracic radiologists, oncologists, and respiratory physicians. Private referrals through London Bridge Hospital can access this same level of institutional expertise. Every cancer case is discussed with a multidisciplinary team at the London Bridge Hospital chest MDT, which Dr Okiror attends fortnightly. Where a case needs urgent discussion, direct access to specialist colleagues ensures no patient waits a fortnight for a decision that cannot wait. Patients seeking an independent view may request a second opinion →
PET-CT (positron emission tomography combined with CT) measures metabolic activity. Cancerous cells typically show higher glucose uptake than benign tissue, appearing as fluorodeoxyglucose (FDG)-avid lesions on the scan. PET-CT is not infallible — small nodules under 8mm and slow-growing ground-glass lesions may be PET-negative even if malignant — but it provides important additional data for larger, solid nodules.
A PET-CT result, however, is not a diagnosis on its own. The degree of FDG avidity must be interpreted in the context of the nodule's CT characteristics, the patient's risk profile, and prior imaging. This is where the Herder score becomes clinically useful.
The Herder score is a validated clinical prediction model that integrates four variables to estimate the probability that a lung nodule is malignant:
| Factor | Variable | Points |
|---|---|---|
| Nodule diameter | <15mm / 15–30mm / >30mm | 0 / 1 / 3 |
| Spiculation on CT | Not spiculated / Spiculated | 0 / 2 |
| FDG avidity on PET | None / Faint / Moderate / Intense | 0 / 1 / 2 / 3 |
| History of malignancy >5yr prior | No / Yes | 0 / 1 |
The combined score is converted to a probability of malignancy using a logistic regression model. British Thoracic Society guidelines recommend the Herder model when PET-CT has been performed on a solid nodule, because it provides a more precise and reproducible risk estimate than clinical gestalt alone.
The clinical implications are direct. A Herder score yielding a probability below 5% allows confident reassurance — the nodule can be placed on a standard surveillance pathway or discharged. A probability above 65% identifies the nodule as high risk, indicating that watchful waiting is no longer appropriate and that tissue diagnosis or surgical resection should be arranged without delay. Intermediate scores require individualised assessment — weighing the probability of malignancy against the risks and benefits of biopsy, surgery, or continued surveillance for that specific patient.
Importantly, the Herder score is a tool to support clinical decision-making — not a substitute for it. A patient with a Herder probability of 40% might have clinical or radiological features that make the treating clinician more or less concerned than the score alone suggests. The score informs the conversation; it does not replace it.
A biopsy provides a tissue diagnosis — the only way to know with certainty whether a nodule is benign or malignant. Not every nodule needs a biopsy. Small, low-risk nodules that are stable on surveillance do not. Clearly benign nodules with characteristic calcification or hamartoma features do not. But for intermediate or high-risk nodules that cannot be confidently diagnosed on imaging alone, tissue diagnosis may be the most clinically appropriate next step.
A needle is passed through the chest wall, guided by CT imaging, to sample the nodule. Effective for peripheral nodules close to the chest wall. The main risk is pneumothorax (lung collapse), which occurs in approximately 20–30% of cases. Not suitable for nodules that are small, centrally located, or in areas where the needle path would cross major blood vessels or emphysematous lung.
A camera passed down the throat into the airways can biopsy nodules close to the main airways. However, the majority of lung nodules sit in the outer lung, beyond where a standard camera can reach. EBUS (endobronchial ultrasound) is used to sample lymph nodes and central lesions and is an important tool in lung cancer staging, but is not designed for peripheral nodule biopsy.
ION is a robotic navigation system that uses a shape-sensing, ultra-thin flexible catheter to navigate through the airways — guided by a pre-procedural CT roadmap and confirmed by real-time cone-beam CT imaging — to reach nodules in the peripheral lung. It is designed specifically for the nodules that standard bronchoscopy cannot reach.
London Bridge Hospital was the first private hospital in Europe to introduce ION bronchoscopy in routine clinical practice outside NHS research trials. At Guy's and St Thomas', the ION programme has carried out 632 navigational bronchoscopy procedures since April 2025, with diagnostic yields of 76–89% across a range of nodule sizes and a pneumothorax rate of approximately 2%. For many patients with intermediate-risk nodules, the Lung Nodule Precision Pathway and ION offer a definitive tissue answer in a single day-case procedure, replacing months of surveillance uncertainty. ION bronchoscopy at London Bridge Hospital →
The majority of patients with a lung nodule do not need surgery. Surgery is indicated where a biopsy has confirmed lung cancer and surgery offers the best chance of cure, or where a nodule has features that make malignancy sufficiently likely that surgical resection is both diagnostic and therapeutic.
Two major international trials — JCOG0802 and CALGB 140503 — have confirmed that for small, early-stage tumours (typically under 2cm), a segmentectomy achieves equivalent cancer control to a lobectomy while preserving significantly more healthy lung tissue. This means less breathlessness, better exercise capacity, and faster recovery. For patients with emphysema, COPD, or reduced lung reserve, a segmentectomy may make surgery possible when a lobectomy would not be safe.
Robotic surgery enables the precision that makes segmentectomy reliably reproducible. At Guy's and St Thomas', 71.3% of anatomic resections were performed robotically in 2024–25 — more than double the national average of 24% — with an operative survival rate of 99.59% against a national benchmark of 98.5%. Only 6% of resections were wedge resections, compared to 14% nationally — reflecting a deliberate commitment to anatomically precise, lung-sparing surgery. Robotic lung surgery at London Bridge Hospital →
Where ION bronchoscopy is used to biopsy a nodule, a small fluorescent dye marker can be placed at the exact nodule site during the same procedure. If surgery is subsequently needed, the da Vinci robotic system’s infrared camera detects that marker, guiding the resection precisely to the nodule — enabling a segmentectomy rather than a lobectomy in many cases. This integrated diagnostic and surgical pathway, available privately at London Bridge Hospital, means patients move from uncertainty to definitive treatment as efficiently as possible, with the smallest operation appropriate for their situation.
If you have been told you have a lung nodule and want expert assessment without delay, private consultation is available at London Bridge Hospital (SE1) and The Lister Hospital Chelsea (SW1). Self-referrals welcome. Most new patients are seen within 2–3 days of contacting the practice.
At a first consultation, your CT scan images are reviewed personally and in full — not just the written report. A clear plan is agreed at that appointment. You will not leave without knowing exactly what the next step is, whether that is reassurance, a surveillance scan, a Herder score calculation following PET-CT, or further investigation.
The private pathway draws on the clinical infrastructure of Guy's and St Thomas' NHS Foundation Trust — the UK's largest thoracic surgical programme, with outcome data that consistently exceeds the national benchmark. Patients who have had a targeted lung health check result and want faster certainty than the NHS surveillance pathway offers should see the dedicated targeted lung health check guide →
What is a lung nodule?
A lung nodule is a small, rounded area of tissue — typically less than 3cm in diameter — that appears as a white spot on a CT scan. The vast majority are entirely benign. Only a small minority represent early-stage lung cancer.
Does a lung nodule mean I have cancer?
Almost certainly not. Around 15 in every 100 people scanned through the NHS Lung Cancer Screening Programme are found to have lung nodules — and the vast majority are benign. Of all people invited to the programme, approximately 1 in 278 are ultimately diagnosed with lung cancer — and the actual rate among those who attended for scanning is higher, as the denominator is invitees, not attendees. Every nodule deserves expert assessment rather than assumption.
What size lung nodule is concerning?
Nodules under 6mm are generally very low risk. Nodules between 6mm and 8mm warrant a repeat CT at 3 months. Nodules over 8mm — particularly those with irregular edges, ground-glass appearance, or demonstrable growth — require more urgent specialist assessment, which may include PET-CT and the Herder score. These thresholds are a guide, not a rigid protocol — the full clinical picture always matters.
What is the Herder score and does my nodule need one?
The Herder score is a validated clinical prediction model that estimates the probability that a lung nodule is malignant, using PET-CT FDG avidity, nodule size, CT morphology, and prior cancer history. It is recommended by the British Thoracic Society for use when PET-CT has been performed on a solid nodule over 8mm. A Herder probability below 5% allows confident reassurance; above 65% indicates high risk requiring tissue diagnosis or resection. If your nodule has had a PET-CT and no one has discussed a formal probability score with you, that is a reason to seek expert review.
Why do T1a, T1b and T1c lung cancers have different survival rates?
Stage I lung cancer is not a uniform category. IASLC data from 77,156 patients (8th edition, Rami-Porta et al., JTO 2015) demonstrates that five-year survival differs significantly within Stage I based on tumour size alone: T1a (≤1cm) 92%, T1b (>1–2cm) 83%, T1c (>2–3cm) 76%. The 9th edition (Van Schil et al., JTO 2024) validated exactly the same cut-points across 124,581 patients. The gradient is confirmed. From 1cm to 3cm, every centimetre counts.
What is the difference between a lung nodule and a lung mass?
A lung nodule is 3cm or less in diameter. Anything larger is classified as a lung mass, which carries a significantly higher probability of malignancy and requires urgent investigation.
What is ION bronchoscopy and how does it help?
ION bronchoscopy is a robotic navigation system that guides an ultra-thin catheter through the airways to reach and biopsy nodules deep in the outer lung — areas previously inaccessible without surgery. A cone-beam CT confirms the exact position before any sample is taken. London Bridge Hospital was the first private hospital in Europe to introduce ION in routine clinical practice, and the pathway is actively accessible to private patients within days.
How quickly can I be seen privately for a lung nodule in London?
New private patients are typically seen within 2–3 days. Self-referrals welcome. Contact Jo Mitchelson on 020 7952 2882 or pa@lungsurgeon.co.uk. Consultations at London Bridge Hospital (SE1) and Lister Hospital Chelsea (SW1).
What is a segmentectomy and is it as effective as removing the whole lobe?
A segmentectomy removes one anatomical segment of the lung rather than an entire lobe. For small, early-stage tumours, two major international trials (JCOG0802 and CALGB 140503) have confirmed it achieves equivalent cancer control to a full lobectomy while preserving significantly more healthy lung tissue. At GSTT, robotic surgery enables this precision operation routinely — 71.3% of anatomic resections are performed robotically, more than double the national average.
Self-referrals welcome. Dr Okiror reviews your scan personally at your first appointment and gives you a clear plan — including a Herder score where PET-CT has been performed — not a further wait.
Request a consultation →Sources and references
British Thoracic Society Guidelines for the investigation and management of pulmonary nodules (BTS, 2015, updated 2023) · Rami-Porta et al., The IASLC Lung Cancer Staging Project: Proposals for the Revisions of the T Descriptors in the Forthcoming Eighth Edition of the TNM Classification for Lung Cancer, Journal of Thoracic Oncology, 2015 · Van Schil et al., The IASLC Lung Cancer Staging Project for the 9th Edition of the TNM Classification, Journal of Thoracic Oncology, 2024 · Herder et al., Clinical prediction model to characterize pulmonary nodules: validation and added value of 18F-fluorodeoxyglucose positron emission tomography, Chest, 2005 · Lee et al., Implementation of the NHS England Lung Cancer Screening Programme over 5 years, Nature Medicine, 23 March 2026 · Altorki et al., CALGB 140503 trial, New England Journal of Medicine, 2023 · Saji et al., JCOG0802 trial, The Lancet, 2022 · SUMMIT trial, The Lancet, 2025 · LUNGIMPACT trial, March 2026 · SCTS National Thoracic Surgery Audit 2024–25 · National Lung Cancer Audit State of the Nation Report 2026 (NATCAN)